Hydrogeochemical Characterization of the Urban Coastal Aquifers of Napoli
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DOI: 10.7343/as-2019-375 Technical report Hydrogeochemical characterization of the urban coastal aquifers of Napoli (southern Italy): an overview Caratterizzazione idrogeochimica degli acquiferi urbani costieri dell’area di Napoli (sud Italia): sintesi preliminare Alfonso Corniello, Daniela Ducci Riassunto: I fenomeni di intrusione marina nelle falde idriche Abstract: The presence of phenomena of salt water intrusion in aqui- di zone costiere urbanizzate rappresentano un serio problema in fers located in coastal urbanized areas, especially depended on the use relazione al regime di utilizzo della risorsa. Lo studio ha preso of groundwater, is a widespread problem in the world. The study deals in esame l’estesa fascia costiera del Comune di Napoli (Italia me- with the large coastal belt of the Municipality of Naples(southern Italy), ridionale) il cui territorio è compreso tra le aree vulcaniche del located between the volcanic areas of the Somma-Vesuvius (East) and the Somma-Vesuvio (ad est) e dei Campi Flegrei (ad ovest). In questa Phlegrean Fields (West). Three different coastal sectors were analysed: fascia costiera sono stati individuati e analizzati tre diversi setto- the plain of Bagnoli-Fuorigrotta (BF), the area of Mount Echia (E) ri: la piana di Bagnoli-Fuorigrotta (BF), l’area di Monte Echia (E) and the area of Eastern Naples (EN). Acquired chemical data allowed e la piana ad oriente di Napoli (EN). I dati chimici hanno posto of the identification of three different groundwater chemical features and in risalto nei tre settori l’assenza di intrusione marina principal- the prevalent absence of sea water contamination, mainly due to the low mente per il basso utilizzo delle falde locali. Tuttavia in que- use of these waters. The study highlighted the chief role of the presence of sti tre settori le caratteristiche chimiche delle acque sotterranee faults in this volcanic area, favouring the upwelling of gases (prevalently sono risultate assai diverse. Tale diversità è legata, per le prime CO2). These gases increase the groundwater reactivity causing, in the due aree, al ruolo delle faglie che, anche in relazione al contesto Mount Echia sector, the presence of sulphurous mineral waters and, in vulcanico generale, favoriscono la risalita di gas profondi (pre- the Bagnoli-Fuorigrotta sector, determining the alteration of the natural valentemente CO2). Questi, aumentano la reattività delle acque relationship between freshwater and saltwater. Moreover, in the Eastern sotterranee verso le rocce serbatoio determinando, nella zona di Naples sector, the occurrence of lenses of peat, which play an important Monte Echia, l’origine di acque minerali sulfureo-ferruginose; hydrogeologic role as aquiclude, can determine reducing condition in the nella piana di Bagnoli-Fuorigrotta la risalita di gas interagisce aquifers, with high concentrations in Fe and Mn. invece con l’interfaccia acqua dolce/acque marina causando, nella prima, anche una contaminazione marina non di origine antro- pica. Infine, nella piana ad oriente di Napoli, la diffusa presenza di lenti di torba, che a luoghi agiscono anche da aquiclude, de- termina nel sottosuolo ambienti riducenti con acque sotterranee caratterizzate da alte concentrazioni di Fe e Mn. Keywords: coastal aquifers, hydrochemistry, urban groundwater. Parole chiave: acquiferi costieri, idrogeochimica, idrogeologia urbana. Introduction The territory of the city of Napoli, stretched for about 117 km 2, is mainly hilly and it consists of tuffs and loose pyroclastics linked to the Phlegrean volcanism. The municipal Daniela DUCCI area intercepts three groundwater bodies (GWBs – 2000/60/ Department of Civil, Architectural and Environmental Engineering - University of Naples Federico II, Italy EC, Italian Law: D. Lgs: 152/2006). The volcanic Phlegrean [email protected] Field GWB (Campi Flegrei - FLE) covers the 67 % of the Municipality, while the Eastern Plain of Naples GWB (Piana Alfonso CORNIELLO ad Oriente di Napoli - P-NAP) the 26 % and the Somma- Department of Civil, Architectural and Environmental Engineering - University of Naples Federico II, Italy Vesuvius GWB (Somma Vesuvio - VES) only a small part [email protected] (7 %) (Fig. 1). The coastal strip, with the exception of the tufaceous hills Ricevuto/Received: 21 January 2019-Accettato/Accepted: 08 March 2019 of Posillipo (Figs. 1 and 2) and San Martino (Fig. 3), is formed Pubblicato online/Published online: 29 March 2019 by plains, more or less wide, in which loose pyroclastics This is an open access article under the CC BY-NC-ND license: (eroded by the hilly sector), alluvial and / or marine sediments http://creativecommons.org/licenses/by-nc-nd/4.0/ are present and often host the final part of the wider three groundwater bodies. © Associazione Acque Sotterranee 2019 Acque Sotterranee - Italian Journal of Groundwater (2019) - AS28- 375: 11 - 19 11 DOI: 10.7343/as-2019-375 Fig. 1 - The Municipality of Naples (in yellow). In red the three groundwater bodies and in the green squares the three studied coastal areas. In blue, the groundwater levels contour lines (m a.s.l.) of the year 2003. Fig. 1 - Il Comune di Napoli (in giallo). In rosso i tre Corpi Idrici sotterranei e nei riquadri verdi le tre aree costiere studiate. In blu i livelli delle acque sotterranee nell’anno 2003 (m s.l.m.). Unlike what happens in other coastal urbanized areas and VES, both constituted by volcano-pyroclastic deposits, (Gangopadhyay and Das Gupta 1995; Bocanegra et al. 2010; present a radial groundwater flow (respectively at West Custodio 2010; Werner 2010; Di Sipio and Zezza 2011; and East), while in the P-NAP, prevalently alluvial, the Thorn 2011; Dentoni et al. 2015), groundwater does not groundwater flow direction is NE-SW, originating at the foot show phenomena of salt water intrusion, above all due to the of the carbonate mountains. low use of these waters (Comune di Napoli 1993; Ducci and The study is focused on three areas (Fig. 1), two plains Sellerino 2015). (Bagnoli-Fuorigrotta BF and Eastern Naples EN) and the final The aim of this paper is the preliminary identification and part toward the sea of the hilly part of the city (Mount Echia E). the hydrogeochemical characterization of the urban coastal aquifers of Napoli, highlighting the differences between the The plain of Bagnoli-Fuorigrotta three coastal zones. The plain of Bagnoli-Fuorigrotta falls in the FLE Hydrogeological Settings of the Study Area groundwater body and it stretchs for about 4 km (from The investigated area is very complex from the geological SW to NE) in the western sector of the city of Napoli; the point of view. There are many papers describing the geology tuffaceous Posillipo hill is its southeastern border. and the volcanological history of the Neapolitan area. A The area falls into the caldera of the eruption of the recent summary is in Carlino (2019). The hydrogeology of Neapolitan Yellow Tuff (NYT - 15 ky b.p.; Deino et al. the area is detailed in local and specific studies (Celico et 2004). The Posillipo hill represents the outcropping border al. 2001; Corniello et al. 2000; Ducci and Sellerino 2015; of the caldera and at its base the NYT is lowered by faults Sellerino et al. 2019). (Russo et al. 1998 - Fig. 2). In the Municipality of Naples, despite the presence of three The pyroclastics ejected from the Agnano-Monte Spina groundwater bodies, the groundwater flow seems uniform, eruption (4.1 ky b.p.), in the north-western area of the plain, from N toward the coast. The differences among the three were reworked in different times in continental or marine groundwater bodies are more evident upstream, where FLE environments. 12 Acque Sotterranee - Italian Journal of Groundwater (2019) - AS28- 375: 11 - 19 DOI: 10.7343/as-2019-375 Mount Echia Mount Echia (Fig. 3) is a small tufaceous hill that falls in the FLE groundwater body and it stretches, from the sea towards NW, up to the San Martino hill, separating the area where is the Royal Palace of Neaples (Palazzo Reale) from the plain on the west (Riviera di Chiaia - BB’ in Fig. 3). At the southern foot of Mount Echia, near the coastline, the sulphurous Spring of Chiatamone S.P.A. (E3 in Fig. 3) was present and it has been closed in 1973, due to water pollution (Corniello et al. 2000). Fig. 2 - Hydrogeological setting of the Bagnoli-Fuorigrotta plain. 1) Coroglio-Tren- taremi tuffs; 2) Neapolitan Yellow Tuff: 3) Nisida volcano tuffs; 4) Astroni volcano pyroclastics; 5) marshy deposits and post roman age pyroclastics; 6) pyroclastics and al- luvial deposits; 7) loose debris; a) faults; b) drillings; c) groundwater levels contour lines (m a.s.l., May 2009; from DIGA 2009); d) groundwater sampling points (Tab. 1). Fig. 2 - Assetto idrogeologico della piana di Bagnoli-Fuorigrotta. 1) Tufi di Coroglio-Trentaremi; 2) Tufo Giallo Napoletano; 3) Tufi del vulcano di Nisida; 4) depositi di palude e piroclastiti di età post-romana; 5) piroclastiti e depositi alluvionali; 6) detriti di versante; a) faglie; b) perforazioni; c) livelli delle acque sotterranee (in m s.l.m.; Maggio 2009; DIGA 2009); d) punti di campionamento delle acque sotterranee (Tab. 1). Fig. 3 - The area of Mount Echia. Hydrogeological sections and the map of the area In the subsoil are present volcanites and, in the SW part, showing the traces of the sections and the groundwater sampling points (blue dots, in red alluvial and marshy deposits and post-Roman pyroclastics for mineral water; Tab. 1). (Fig. 2). The NYT is the bedrock in the eastern and central Fig. 3 - L’area del Monte Echia. Sezioni idrogeologiche e pianta con le tracce di sector of the plain while, in the western sector, it is absent, sezione e i punti di campionamento delle acque sotterranee (punti blu, rossi per probably due to the Agnano-Monte Spina eruption. le acque minerali; Tab. 1).